Re: UL system for Microwave oven transformers
Peter, We are checking with Dupont's expert to see if what we are concerned now for the 600V or 300V system refers to the input voltage (primary winding voltage) only. Perhaps you are right, thanks. But if you can cite any good source to support this, that would be much helpful to us. For the construction guidlines, please let me know which UL standard we should follow. I just contacted UL Hong Kong that they have no idea on it. Initially, they suggested UL-1585 for the design standard for microwave oven transformers. But they informed me that they have made a mistake and even they would need time to check. Perhaps you have some idea, right? Robin Chan. Dear Robin, If I'm not mistaken the 300 V or 600 V rating for Insulation Systems per UL1446 is for primary supply voltage and not for the maximum voltage in any winding. You state that the transformer is being designed for a 200 C rating. Remember that you need only comply with UL1446 if your transformer winding temperatures exceed the Class A insulation system permitted temperature rises in the Microwave and/or applicable transformer standards under normal and abnormal conditions. Once you have determined that you need a higher than Class A insulation system, best and cheapest way to obtain a UL1446 compliant system is to have UL conduct Sealed Tube Testing on your system and an adopted system from Nomex manufacturer (I believe it is EI Dupont) using identical major insulation system parts (ground insulation is a major part). Nomex manufacturer will be very happy to give you a letter authorising UL the use of the information in their file to grant your company Recognition for your system employing their major insulation materials. Best Regards, Dear everybody, We are now designing a transformer for microwave oven. Here is the basic spec, input voltage: 120V rms output voltage: 2300V rms Thermal class: 200C We are facing the problem that we need to be compliace with UL1446 and UL 1585. They specify that all ground insulation need to be at least 5 mil Nomex for a 600V system. Then for 2300V system, by scaling the thickness of Nomex, do we need to increase the thickness to 18-20mil Nomex. Well, we can use Nomex at that thick but the cost of the whole unit becomes very high, any comments? Robin Chan. email: ro...@alumni.cuhk.edu.hk - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). __ Get Your Private, Free Email at http://www.hotmail.com - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: UL system for Microwave oven transformers
Dear Robin, If I'm not mistaken the 300 V or 600 V rating for Insulation Systems per UL1446 is for primary supply voltage and not for the maximum voltage in any winding. You state that the transformer is being designed for a 200 C rating. Remember that you need only comply with UL1446 if your transformer winding temperatures exceed the Class A insulation system permitted temperature rises in the Microwave and/or applicable transformer standards under normal and abnormal conditions. Once you have determined that you need a higher than Class A insulation system, best and cheapest way to obtain a UL1446 compliant system is to have UL conduct Sealed Tube Testing on your system and an adopted system from Nomex manufacturer (I believe it is EI Dupont) using identical major insulation system parts (ground insulation is a major part). Nomex manufacturer will be very happy to give you a letter authorising UL the use of the information in their file to grant your company Recognition for your system employing their major insulation materials. Best Regards, Date sent: Thu, 10 Dec 1998 20:05:09 +0800 From: Robin Chan ro...@alumni.cuhk.edu.hk Organization: The Chinese University of Hong Kong To: emc-p...@ieee.org Subject:UL system for Microwave oven transformers Send reply to: Robin Chan ro...@alumni.cuhk.edu.hk Dear everybody, We are now designing a transformer for microwave oven. Here is the basic spec, input voltage: 120V rms output voltage: 2300V rms Thermal class: 200C We are facing the problem that we need to be compliace with UL1446 and UL 1585. They specify that all ground insulation need to be at least 5 mil Nomex for a 600V system. Then for 2300V system, by scaling the thickness of Nomex, do we need to increase the thickness to 18-20mil Nomex. Well, we can use Nomex at that thick but the cost of the whole unit becomes very high, any comments? Robin Chan. email: ro...@alumni.cuhk.edu.hk - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). PETER S. MERGUERIAN MANAGING DIRECTOR PRODUCT TESTING DIVISION I.T.L. (PRODUCT TESTING) LTD. HACHAROSHET 26, P.O.B. 211 OR YEHUDA 60251, ISRAEL TEL: 972-3-5339022 FAX: 972-3-5339019 E-MAIL: pe...@itl.co.il Visit our Website: http://www.itl.co.il - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: UL system for Microwave oven transformers
Robin, You do not scale the thickness as such when increasing the voltage rating. Insulation Thickness is directly related to the degree of Mechanical protection that needs to be achieved. Insulation thickness is only partially (brain stoppage for lack of a better word!) related to voltage rating. UL generally requires a higher degree of mechanical protection for insulation (and wire insulation) as the voltage rating increases. In addition, voltage tests (such as Dielectric strength, Insulation Resistance, and such) apply and require higher values as the desired voltage rating is increased. Typically, many Insulation materials will not be required to increase their minimum thickness requirements above 600 Volts values, as long as all test requirements are met. I recommend you discuss your nomex options and thickness limitations with your NRTL and/or your Nomex supplier. You can reach me directly if you wish, as well. Hope this helps, Regards, Bob Tims Compliance Engineer Ericsson Messaging Systems Inc. robert.t...@ericsson.com - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
